The purpose of this article is to analyze the voltage drop in the contact network caused by poor-quality operation of an alternating current electric locomotive when passing heavy trains. Heavy-haul traffic is considered today as a valid and necessary tool for increasing weight norms and increasing the throughput of railway sections. The article provides statistics on the passage of heavy and connected trains on the Krasnoyarsk railway for 2019 and 2020. For the effective use of heavy traffic, it is necessary to solve a number of problems, one of which is to reduce the voltage in the overhead network when passing heavy trains, this negatively affects the speed of the train along the haul, the conditions for cooling the power equipment of the electric locomotive deteriorate, etc. As a result of the analysis of the operation of the thyristor rectifier-inverter converter, a number of disadvantages were revealed. The reason for the low power factor of the electric locomotive lies in the use of an outdated element base based on thyristors, their closure is carried out only in the next voltage half-cycle, long-term switching and a large opening angle of thyristors leads to a significant reactive current in the contact network. Based on the analysis the voltage losses at the current collector, it was concluded that it is necessary to reduce the duration of the switching process of the arms of the rectifier-inverter converter, in which a short circuit occurs in the secondary winding of the traction transformer. An alternative version of the converter based on fully controlled semiconductor devices - IGBT transistors is proposed. The ability to open and close at any time of such elements allows you to minimize the phase angle and increase the power factor. Due to the almost instantaneous switching of transistors, the distortion in the contact network is minimized.